This invention generally relates to electrochemical systems for storage and release of electrical energy. In particular, the present invention relates to electrochemical systems for use in electronic circuits, for example, as capacitors or batteries. More particularly, the present invention relates to electrochemical systems for operation in electronic circuitry, for example, as capacitors or batteries, with either a non-liquid, organic solution, aqueous solution or a protonic medium electrolyte material positioned between the electrodes.
Further still, the present invention relates to improved designs for bi-polar assemblies that address the deficiencies in existing bi-polar designs. In particular, this invention relates to an assembly of a plurality of single cells of an electrochemical system.
As electronic devices and other electrical apparatuses become increasingly more portable and provide more functionality, advances must be made in the devices of such devices that enable such portability. As is often the case with current electronics technology, the limiting factor in both size and functionality of an electronic apparatus is the size and weight of its component parts. In particular, the size and weight of its energy storage components. Additionally, the miniaturization of electronics has seen the push towards integrating various components into a single device to save both room and weight within both portable and stationary devices.
The current main energy source used for portable electronics is the electrochemical battery and/or the electrochemical capacitor. One of the limiting features of such current energy storage devices is the packaging of the electrochemical system. Prior art enclosures for flat and low height designs have suffered from several disadvantages. Coin cells for round shaped assemblies have needed to be crimped or swagged closed which requires expensive precision tooling. Further, such a method of enclosure requires accurate placement and/or control of closing pressures which can be very time consuming. Prismatic cell designs for rectangular and square shaped assemblies require precise corner radii and equivalent closing force across the entire area of the design to ensure good contact between the casing and the internal cells. While useful for their purpose, these prior art designs have forced higher production costs and longer production times due to the precision and technically complex assembly methods.
Further, in both coin and prismatic designs a grommet is needed to prevent shorting between the two poles of the electrochemical system. Should the electrochemical device consist of a plurality of cells in a stack then the grommet must serve to insulate the edge of the pack from the enclosure and insulate the two portions of the enclosure that contact the two poles of the device. Thus the grommet acts to prevent the manufacture of some desirable forms of connections to a plurality of cells.
It is, therefore, desirable to provide a multi-cell energy storage device which may comprise either an electrochemical capacitor, a double-layer capacitor or a battery. In an electrochemical capacitor version of the present invention, which may also be referred to as a pseudo-capacitor or batcap, the electrodes comprise material that may participate in reversible charge transfer reactions. Thus, a portion of the energy is stored in the double-layer at the surface of the electrodes and another portion is contributed by the charge transfer reactions. In a double-layer capacitor version of the present invention, essentially all of the energy is stored in the double layer at the surface of the electrodes. In a battery version of the present invention, the anode and cathode materials are specifically chosen so that each reacts during operation of the cell. The chemical energy that is stored in the electrodes is converted to electrical energy via charge transfer reactions of active materials. It is also desirable to provide a new packaging for an electrochemical single or multi-cell energy storage device wherein the cells in a multi-cell design may be in series, parallel or a combination thereof by virtue of the device""s construction in one integrated structure.
The present invention recognizes and addresses various of the foregoing limitations and drawbacks, and others, concerning both the design of an electrochemical single or multi-cell energy storage device and methods of packaging the same. Therefore, the present invention provides an improved electrochemical single or multi-cell energy storage device and outer packaging for the same.
It is, therefor, a principle object of the subject invention to provide an improved electrochemical single or multi-cell energy storage device. More particularly, it is an object of the present invention to provide an electrochemical single or multi-cell energy storage device within an improved casing. In such context, it is still a more particular object of the present invention to provide an electrochemical single or multi-cell energy storage device wherein the improved casing comprises a pre-formed metal sheet.
Still further, it is a principle object of this invention to provide an improved single layer, electrically conductive casing for an electrochemical single or multi-cell energy storage device. It is a further object of the present invention to provide such an improved electrochemical single or multi-cell energy storage device and casing which are simple and cost-effective to manufacture. In such context, it is an object of the present invention to provide a electrochemical single or multi-cell energy storage device and improved casing which exhibits a low equivalent series resistance (hereinafter ESR) and a low internal and contact resistance within the internal stack of the device and between the internal stack and the casing, respectively.
Additional objects and advantages of the invention are set forth in, or will be apparent to those of ordinary skill in the art from, the detailed description as follows. Also, it should be further appreciated that modifications and variations to the specifically illustrated and discussed features and materials hereof may be practiced in various embodiments and uses of this invention without departing from the spirit and scope thereof, by virtue of present reference thereto. Such variations may include, but are not limited to, substitutions of the equivalent means, features, and materials for those shown or discussed, and the functional or positional reversal of various parts, features, or the like.
Still further, it is to be understood that different embodiments, as well as different presently preferred embodiments, of this invention, may include various combinations or configurations of presently disclosed features, elements, or their equivalents (including combinations of features or configurations thereof not expressly shown in the figures or stated in the detailed description).
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the principles of the invention.
In one exemplary embodiment, there may be provided a multi-cell capacitor which comprises a carbon/plastic composite film coated with a metallic film on its external side as a terminal current collector, a plurality of non-conductive pre-formed isolating frames and within the openings formed in each of the perforated isolating frames is present a high surface area carbon-based electrode to form capacitive electrode plates.
A bi-polar assembly, for use internal to stack of series bi-polar connected cells, comprises a bi-polar current collector, such as a single conductive carbon polymer matrix current collector. The bi-polar current collector within each bi-polar assembly need not have a metal film coating. On respective top and bottom sides of each bi-polar current collector in the recesses formed within perforated isolating frames may be placed a high surface area carbon-based electrode paste to form electrode plates.
The capacitor device may be formed by stacking successive layers of a bi-polar current collector and electrodes, the electrodes being separated by proton conductive polymer membranes. The ends of the stacks are terminated with a terminal current collector. The membranes function as a proton conductive layer within each capacitor cell. The stack may be potted, along its periphery only, with an insulating material, such as but not limited to an epoxy, in order to maintain a good seal and prevent ingress of moisture from the ambient environment. An outer conductive casing, such as a pre-formed metal sheet, serves as a shell around the periphery potting material and is in physical contact with the terminal current collectors.
In such a multi-cell electrochemical energy storage device, closure may be made without the use of a grommet and there exists no need for crimping or swagging. The internal cells may be connected in a bi-polar design in series in order to increase the pack voltage. Alternatively, a tongue design may be used to combine two or more bi-polar stacks in parallel within a single casing in order to increase capacity and decrease internal resistance. The outer casing serves as a common pole for each of the stacks and the tongue as a common pole of the opposite polarity.
The casing may be a pair of U-shaped shells fitted over the epoxy-held internal stack or stacks and bonded along the adjoining sides of the shells. In an alternative exemplary embodiment, the casing may be a single sheet of pre-formed metal sheet bent approximate its midpoint to encase the epoxy-held internal stack and bonded along the adjoining ends of the foil sheet. In yet another exemplary embodiment, the casing may be a tube-shape. In any exemplary embodiment, the outer casing may be bent to form a pre-loaded structure that applies a spring-like loading to the shell in order to improve the contact between the shell and the stack and to offset thermal expansion cycles.